Ambient light suppression

ABSTRACT

According to an aspect, there is provided a system (200) comprising: an image projection unit (210) configured to project an illumination pattern onto at least a portion of a scene, an imaging unit (220) configured to capture a plurality of images of the scene while the illumination pattern is projected onto the scene, and a processing unit (230) configured to: demodulate the plurality of images based on the illumination pattern and with respect to a target section in the plurality of captured images, wherein the target section corresponds to one of: a portion of the scene on which the illumination pattern is selectively projected while the plurality of images were captured, a portion of the scene at which the projected illumination pattern is resolvable, a portion of the scene with pixel depth values which satisfy a predetermined range; and generate an ambient light suppressed image of the scene based on results of the demodulation.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C.§ 371 of International Application No. PCT/EP2021/062136, filed on May7, 2021, which claims the benefit of European Patent Application No.20174915.7 filed on May 15, 2020. These applications are herebyincorporated by reference herein.

FIELD OF THE INVENTION

The present disclosure relates to a system for performing ambient lightsuppression and a method for controlling thereof.

BACKGROUND OF THE INVENTION

There has been considerable development and investment in exploratoryactivities in digital innovation in the field of non-obtrusivemeasurement and monitoring, specifically on skin sensing for personalcare and health applications. Currently known skin measurement systemspromise skin quantification and monitoring of features of skin thatoffer consumers information related to changes that may be too small todetect, too faint to notice, and/or too slow to follow. For thesesystems to be acceptable by consumers, sensing methods and systemsshould be sensitive as well as specific. Additionally, robustness ofmeasurement is essential to build consumer trust. One critical issueassociated with such imaging-based systems, when placed in anuncontrolled environment (e.g. at home) is the undefined and potentiallyvarying ambient lighting.

Modulated imaging techniques, such as spatial frequency domain imaging(SFDI), are techniques that use projections of specific light patterns,phase shifted sinusoid patterns mainly, to generate images that can beused for analysis of skin properties for instance. Three spatiallymodulated images with the same sinusoidal pattern, but phase-shifted,are sufficient to recreate a demodulated AC image where all the DCcomponents of light is excluded, therefore removing the ambient light.Demodulation requires three images of the object of interest I₁, I₂, andI₃ recorded with projection of the sinusoidal pattern with the samespatial frequency, but with ⅔π phase difference each (0, ⅔π, 4/3π). Thedemodulation of the images can be represented by the formulae (1) and(2) below:

$\begin{matrix}{M_{AC} = {\frac{\sqrt{2}}{3}\left( {\left( {I_{1} - I_{2}} \right)^{2} + \left( {I_{2} - I_{3}} \right)^{2} + \left( {I_{1} - I_{3}} \right)^{2}} \right)^{1/2}}} & (1)\end{matrix}$ $\begin{matrix}{M_{DC} = {\left( {I_{1} + I_{2} + I_{3}} \right)/3}} & (2)\end{matrix}$where M_(AC) is the AC component of the image (which can be regarded tocorrespond to the modulated illumination), and M_(DC) is the DCcomponent of the image (which can be regarded to correspond to theambient illumination).

As an example. FIG. 1 illustrates an ambient light correction operationby way of a number of images. Specifically. FIG. 1 includes an initialimage 110, a plurality of modulated images 120A, 120B, and 120C, as wellas demodulated images 130 and 140 which show how ambient light can becorrected for based on a number of modulated images. In the context ofthis disclosure, the term “modulated image” may refer to an image whichdepicts a modulated pattern being projected onto a part of a scene, andthe term “demodulated image” may refer to an image that underwentdemodulation with respect to the depicted modulated pattern.

In the initial image 110, the scene is only illuminated by ambient lightand it can be seen that the face is unevenly illuminated. Each of afirst modulated image 120A, a second modulated image 1208, and a thirdmodulated image 120C is associated with a different phase shift. In thisexample, the first modulated image 120A is associated with a 0° phaseshill, the second modulated image 120B is associated with a 120° phaseshift, and the third modulated image 1200 is associated with a 240°phase shift. The uneven illumination that is presented in the initialimage 110 can be corrected by performing demodulation of the modulatedimages 120A, 120B, and 120C according to formulae (1) and (2) aspresented above, so as to generate an AC component 130 and a DCcomponent 140. Specifically, the three sinusoidal patterns captured inthe three modulated images 120A, 120B, and 120C are demodulated toarrive at the demodulated images 130 and 140, which respectivelycorrespond to the AC component 130 (representing the alternating part ofthe demodulated signal) and the DC component 140 (representing theconstant part of the demodulated signal). In this case, the AC component130 corresponds to the modulated illumination while the scene isilluminated with both the projected modulated illumination and ambientillumination, while the DC component 140 of the image corresponds to theambient illumination while the scene is illuminated with both themodulated illumination and ambient illumination. Accordingly, the ACcomponent 130 may be regarded as an “ambient light corrected/suppressed”version that represents the scene depicted in the initial image 110.

It is noted that US patent application US 2019/0101383 A1 discloses atechnique for determining an object using structured light to overcomeambient light effects. The technique according to US 2019/0101383 A1utilizes structured light of various spatial frequencies.

It is further noted that Bodenschatz et al. in their paper “Diffuseoptical microscopy for quantification of depth-dependent epithelialbackscattering in the cervix” (Journal of Biomedical Optics (vol. 21,no. 6, 1 Jun. 2016) discuss the use of structured light of differentspatial frequencies to make observation at different tissue depths.

SUMMARY OF THE INVENTION

In some smart mirror systems there may be provided an imaging unit (e.g.a cameral for recording images and/or videos of the face or other partsof a user's body for skin analysis. One of the concerns associated withthese systems is the potential or perceived intrusion of privacy. Incurrently known systems, the imaging units do not discriminate between auser and other elements in the background, and even if only the face ofa user is recorded it would still be relatively easy to recognise theuser. For example, in a currently available system blurring is used tohide the region of an image that is not of interest.

According to a first specific aspect, there is provided a system forperforming ambient light suppression, the system comprising: an imageprojection unit configured to project an illumination pattern onto atleast a portion of a scene, wherein the illumination pattern is atime-varying spatially modulated pattern having a predetermined spatialfrequency; an imaging unit configured to capture a plurality of imagesof the scene while the time-varying spatially modulated illuminationpattern having a predetermined spatial frequency is projected onto thescene; and a processing unit configured to: demodulate the plurality ofimages based on the illumination pattern and with respect to a targetsection in the plurality of captured images, wherein the target sectioncorresponds to one of: a portion of the scene on which the illuminationpattern is selectively projected while the plurality of images werecaptured, a portion of the scene at which the projected illuminationpattern is resolvable, a portion of the scene with pixel depth valueswhich satisfy a predetermined range, wherein the target section is apart of the field of view of the imaging unit, and generate an ambientlight suppressed image of the scene based on results of thedemodulation.

In some embodiments, the image projection unit may be configured to onlyselectively project the illumination pattern onto a selected portion ofthe field of view of the imaging unit, and the target sectioncorresponds to a portion of the scene on which the illumination patternis selectively projected. In these embodiments, the processing unit maybe configured to demodulate the plurality of images with respect to thetarget section such that the generated ambient light suppressed image ofthe scene only depicts one or more elements included in the selectedportion of the field of view of the imaging unit.

In some embodiments the imaging unit may be configured to capture theplurality of images of the scene at a predetermined focal depth, thepredetermined spatial frequency of the illumination pattern and thepredetermined focal depth of the imaging unit being selected such thatthe illumination pattern is only resolvable within a certain distancefrom the focus of the imaging unit, and wherein the target sectioncorresponds to a portion of the scene at which the projectedillumination pattern is resolvable. In these embodiment, the processingunit may be configured to demodulate the plurality of images withrespect to the target section such that the generated ambient lightsuppressed image of the scene only depicts one or more elements includedin field of view within the certain distance range from the focus of theimaging unit.

In some embodiments, the processing unit may be configured to analysethe plurality of images to determine 3D depth information of the scene.The 3D depth information may comprise depth values for each of thepixels of the plurality of images and the target section may be based onthe 3D depth information of the scene. In these embodiments, theprocessing unit may be configured to generate the ambient lightsuppressed image of the scene by only outputting the demodulationresults with respect to the target section.

In some embodiments, the processing unit may be configured to determinethe target section by applying a phase mask to the plurality of images.

In some embodiments, the illumination pattern may comprise aphase-shifting sinusoidal pattern, and the imaging unit may beconfigured to capture the plurality of images at a predetermined phasedifference with respect to the phase of the sinusoidal pattern.

In some embodiments, the illumination pattern may further comprise atleast one phase ramp of a predetermined step size.

In some embodiments, the imaging unit may be configured to capture,while the illumination pattern is projected onto the scene, three setsof images. In these embodiments, a first set of the three sets of imagesmay correspond to a 0° phase shift of the sinusoidal pattern, a secondset of the three sets of images may correspond to 120° phase shift ofthe sinusoidal pattern, and a third set of the three sets of images maycorrespond to 240° phase shift of the sinusoidal pattern.

In some embodiments, the imaging unit may comprise a colour camera andeach of the first, second, and third set of images may comprise a singleimage.

In some embodiments, each of the first, second and third set of imagesmay comprise three images. The first image in each of the three of setsof images may correspond to the red colour channel, the second image ineach of the three sets of images may correspond to the green colourchannel, and the third image in each of the three sets of images maycorrespond to the blue colour channel.

In some embodiments, the processing unit may be configured to demodulatethe plurality of image to produce a first image corresponding to the ACcomponent and a second image correspond to the DC component. In theseembodiments, the first image may be selected as the ambient lightsuppressed image of the scene.

According to a second specific aspect, there is provided a method forcontrolling a system to perform ambient light suppression. The systemcomprises an image projection unit, an imaging unit, and a processingunit, and the method comprises, projecting, by the image projectionunit, an illumination pattern onto at least a portion of a scene,wherein the illumination pattern is a time-varying spatially modulatedpattern; capturing, by the imaging unit, a plurality of images of thescene while the time-varying spatially modulated illumination pattern isprojected onto the scene; and demodulating, by the processing unit, theplurality of images based on the illumination pattern and with respectto a target section in the plurality of captured images, wherein thetarget section corresponds to one of: a portion of the scene on whichthe illumination pattern is selectively projected while the plurality ofimages were captured, a portion of the scene at which the projectedillumination pattern is resolvable, a portion of the scene with pixeldepth values which satisfy a predetermined range; and generating, by theprocessing unit, an ambient light suppressed image of the scene based onresults of the demodulation.

In some embodiments, projecting the illumination pattern onto at least aportion of the scene may comprise only selectively projecting theillumination pattern onto a selected portion of the field of view of theimaging unit. In these embodiments, the target section may correspond toa portion of the scene on which the illumination pattern is selectivelyprojected. Also, in these embodiments, demodulating the plurality ofimages with respect to the target section may be performed such that thegenerated ambient light suppressed image of the scene only depicts oneor more elements included in the selected portion of the field of viewof the imaging unit.

In some embodiments, the illumination pattern may have a predeterminedspatial frequency, and the capturing the plurality of images of thescene may be performed at a predetermined focal depth. In theseembodiments, the predetermined spatial frequency of the illuminationpattern and the predetermined focal depth of the imaging unit may beselected such that the illumination pattern is only resolvable within acertain distance from the focus of the imaging unit, and the targetsection may correspond to a portion of the scene at which the projectedillumination pattern is resolvable. Furthermore, demodulating theplurality of images with respect to the target section may be performedsuch that the generated ambient light suppressed image of the scene onlydepicts one or more elements included in field of view within thecertain distance range from the focus of the imaging unit.

According to a third specific aspect, there is provided a computerprogram product comprising a computer readable medium, the computerreadable medium having computer readable code embodied therein, thecomputer readable code being configured such that, on execution by asuitable computer or processor, the computer or processor is caused toperform the method as described herein.

These and other aspects will be apparent from and elucidated withreference to the embodiment(s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will now be described, by way of example only,with reference to the following drawings, in which:

FIG. 1 illustrates an example of ambient light correction operation byway of a number of images;

FIG. 2 shows a block diagram of a system according to an embodiment;

FIG. 3 illustrates a method for controlling a system to perform ambientlight suppression, according to an embodiment;

FIG. 4 illustrates an ambient light suppression operation by way of anumber of images, according to an embodiment;

FIG. 5 illustrates an ambient light suppression operation by way of anumber of images, according to another embodiment;

FIG. 6 illustrates an ambient light suppression operation by way of anumber of images, according to another embodiment;

FIG. 7 illustrates an ambient light suppression operation according toanother embodiment; and

FIG. 8 illustrates a result of an ambient light suppression operationaccording to an embodiment compared with other imaging or processingtechniques.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As noted above, there is provided an improved system for per formingambient light suppression and a method for controlling thereof, whichaddress the existing problems.

FIG. 2 shows a block diagram of a system 200 according to an embodiment,which can be used for performing ambient light suppression, specificallyfor ambient light suppression in images. As illustrated in FIG. 2 , thesystem comprises an image projection unit 210, an imaging unit 220, anda processing unit 230.

The image projection unit 210 is configured to project an illuminationpattern onto at least a portion of a scene. The illumination pattern isa time-varying spatially modulated pattern, and may comprise aphase-shifting sinusoidal pattern. In addition, in some embodiments theillumination pattern may further comprise at least one phase ramp of apredetermined step size. In some embodiments, the illumination patternmay have a predetermined spatial frequency and/or a predeterminedwavelength. Furthermore, in some embodiments the image projection unit210 may be configured to project the illumination pattern in a mannerthat is focused on an object plane of the scene.

In some embodiments, the image projection unit 210 may be configured toonly selectively project the illumination pattern onto a selectedportion of the field of view of the imaging unit.

The imaging unit 220 is configured to capture a plurality of images ofthe scene while the time-varying spatially modulated illuminationpattern is projected onto the scene. The imaging unit 220 may beconfigured to capture, while the illumination pattern is projected ontothe scene, three sets of images. In these three sets of images, a firstset may correspond to a 0° phase shift of the sinusoidal pattern, asecond set may correspond to 120° phase shift of the sinusoidal pattern,and a third set of may correspond to 240° phase shift of the sinusoidalpattern.

In some embodiments, the imaging unit comprises a colour camera, andeach of the first, second, and third set of images comprises a singleimage. In some alternative embodiments, each of the first, second andthird set of images may comprise three images. In these alternativeembodiments, the first image in each of the three of sets of images maycorrespond to the red colour channel, the second image in each of thethree sets of images may correspond to the green colour channel, and thethird image in each of the three sets of images may correspond to theblue colour channel.

In some embodiments, the imaging unit 220 may be configured to capturethe plurality of images of the scene at a predetermined focal depth. Insome embodiments where the imaging unit 220 is configured to capture theplurality of images of the scene at a predetermined focal depth andwhere the illumination pattern has a predetermined spatial frequency,the predetermined spatial frequency of the illumination pattern and thepredetermined focal depth of the imaging unit may be selected such thatthe illumination pattern is only resolvable within a certain distancefrom the focus of the imaging unit 220.

As mentioned above, in some embodiments the illumination pattern maycomprise a phase-shifting sinusoidal pattern. In these embodiments, theimaging unit 220 may be configured to capture the plurality of images ata predetermined phase difference with respect to the phase of thesinusoidal pattern.

The processing unit 230 is configured to demodulate the plurality ofimages based on the illumination pattern and with respect to a targetsection in the plurality of captured images. The target sectioncorresponds to one of a portion of the scene on which the illuminationpattern is selectively projected while the plurality of images werecaptured, a portion of the scene at which the projected illuminationpattern is resolvable, a portion of the scene with pixel depth valueswhich satisfy a predetermined range. Furthermore, the processing unit230 is also configured to generate an ambient light suppressed image ofthe scene based on results of the demodulation.

The processing unit 230 may be configured to demodulate the plurality ofimages to produce a first image corresponding to the AC component and asecond image correspond to the DC component. The AC component maycorrespond to the alternating part of a demodulated signal associatedwith the plurality of images, and the DC component may correspond to theconstant part of the demodulated signal. In these embodiments, the firstimage may be selected as the ambient light suppressed image of thescene. It will be appreciated that the demodulation may be performed,for example, using formulae (1) and (2) as presented above withreference to FIG. 1 . It will also be appreciated that other formulaenot explicitly discussed here may be used for obtaining the AC and DCcomponents of the signal, e.g. those associated with Discrete CosineTransform, Fourier transform, etc.

As mentioned above, in some embodiments the image projection unit 210may be configured to only selectively project the illumination patternonto a selected portion of the field of view of the imaging unit. Inthese embodiments, the target section may correspond to a portion of thescene on which the illumination pattern is selectively projected.Moreover, in these embodiments, the processing unit 230 may beconfigured to demodulate the plurality of images with respect to thetarget section such that the generated ambient light suppressed image ofthe scene only depicts one or more elements included in the selectedportion of the field of view of the imaging unit 220.

As mentioned above, in some embodiments where the imaging unit 220 isconfigured to capture the plurality of images of the scene at apredetermined focal depth and where the illumination pattern has apredetermined spatial frequency, the predetermined spatial frequency ofthe illumination pattern and the predetermined focal depth of theimaging unit may be selected such that the illumination pattern is onlyresolvable within a certain distance from the focus of the imaging unit220. In addition, in these embodiments, the target section maycorrespond to a portion of the scene at which the projected illuminationpattern is resolvable, and the processing unit 230 may be configured todemodulate the plurality of images with respect to the target sectionsuch that the generated ambient light suppressed image of the scene onlydepicts one or more elements included in field of view within thecertain distance range from the focus of the imaging unit 220.

In some embodiments, the processing unit 230 may be configured toanalyse the plurality of images to determine three-dimensional (3D)depth information of the scene. The 3D depth information may comprisedepth values for each of the pixels of the plurality of images. Inaddition, in these embodiments, the target section may be based on the3D depth information of the scene. The processing unit 230 may beconfigured to generate the ambient light suppressed image of the sceneby only outputting the demodulation results with respect to the targetsection.

Furthermore, in these embodiments, the processing unit 230 may beconfigured to determine the target section by applying a phase mask tothe plurality of images.

In general, the processing unit 230 can control the operation of thesystem 200 and can implement the method described herein. The processingunit 230 can comprise one or more processors, processing units,multi-core processor or modules that are configured or programmed tocontrol the system 200 in the manner described herein. In particularimplementations, the processing unit 230 can comprise a plurality ofsoftware and/or hardware modules that are each configured to perform, orare for performing, individual or multiple steps of the method describedherein.

Although not illustrated in FIG. 2 , in some embodiments the system 200may further comprise at least one user interface. Alternative or inaddition, at least one user interface may be external to (i.e. separateto or remote from) the system 200. For example, at least one userinterface may be part of another device. A user interface may be for usein providing a user of the system 200 with information resulting fromthe method described herein. Alternatively or in addition, a userinterface may be configured to receive a user input. For example, a userinterface may allow a user of the system 200 to manually enterinstructions, data, or information. In these embodiments, the processingunit 230 may be configured to acquire the user input from one or moreuser interface.

A user interface may be any user interface that enables the rendering(or output or display) of information to a user of the system 200.Alternatively or in addition, a user interface may be any user interfacethat enables a user of the system 200 to provide a user input, interactwith and/or control the system 200. For example, the user interface maycomprise one or more switches, one or more buttons, a keypad, akeyboard, a touch screen or an application (for example, on a tablet orsmartphone), a display screen, a graphical user interface (GUI) or othervisual rendering component, one or more speakers, one or moremicrophones or any other audio component, one or more lights, acomponent for providing tactile feedback (e.g. a vibration function), orany other user interface, or combination of user interfaces.

In some embodiments, the system 200 may comprise a memory. Alternativelyor in addition, one or more memories may be external to (i.e. separateto or remote from) the system 200. For example, one or more memories maybe part of another device. A memory can be configured to store programcode that can be executed by the processing unit 230 to perform themethod described herein. A memory can be used to store information,data, signals and measurements acquired or made by the processing unit230 of the system 200. For example, a memory may be used to store theplurality of captured images, the plurality of candidate images, and/orthe ambient light suppressed image. The processing unit 230 may beconfigured to control a memory to store the plurality of capturedimages, the plurality of candidate images, and/or the ambient lightsuppressed image.

In some embodiments, the system 200 may comprise a communicationsinterface (or circuitry) for enabling the system 200 to communicate withany interfaces, memories and/or devices that are internal or external tothe system 200. The communications interface may communicate with anyinterfaces, memories and/or devices wirelessly or via a wiredconnection. For example, the communications interface may communicatewith one or more user interfaces wirelessly or via a wired connection.Similarly, the communications interface may communicate with the one ormore memories wirelessly or via a wired connection.

It will be appreciated that FIG. 2 only shows the components required toillustrate an aspect of the system 200 and, in a practicalimplementation, the system 200 may comprise alternative or additionalcomponents to those shown.

FIG. 3 illustrates a method for controlling a system to perform ambientlight suppression. The illustrated method can generally be performed bythe system 200, and specifically in some embodiments by or under thecontrol of processing unit 230 of the system 200. For the purpose ofillustration, at least some of the blocks in FIG. 3 will be described inthe following with reference to the various components of the system 200of FIG. 2 .

With reference to FIG. 3 , at block 302, an illumination pattern isprojected onto at least a portion of a scene. The projection may beperformed by the image projection unit 210 of the system 200, and thisprojection may be performed in a manner that is focused on an objectplane of the scene. The illumination pattern is a time-varying spatiallymodulated pattern such as a phase-shifting sinusoidal pattern, and theimagine unit is configured to capture the plurality of images at apredetermined phase difference with respect to the phase of thesinusoidal pattern. In some embodiments, the illumination pattern mayhave a predetermined spatial frequency and/or a predeterminedwavelength. Alternatively or in addition, the illumination pattern maycomprise at least one phase ramp of a predetermined step size.

In some embodiments, projecting the illumination pattern onto at least aportion of the scene at block 302 may comprise only selectivelyprojecting the illumination pattern onto a selected portion of the fieldof view of the imaging unit.

Returning to FIG. 3 , at block 304, a plurality of images of the sceneare captured while the time-varying spatially modulated illuminationpattern is projected onto the scene at block 302. Thus, at least in someembodiments, the steps illustrated in block 302 and block 304 may beregarded as being performed simultaneously. The capturing of theplurality of images may be performed by the imaging unit 220 of thesystem 200.

As mentioned above, in some embodiments the illumination pattern maycomprise a phase-shifting sinusoidal pattern. In these embodiments,capturing the plurality of images at block 304 may be performed at apredetermined phase difference with respect to the phase of thesinusoidal pattern.

In some embodiments, at block 304 three sets of images are capturedwhile the illumination pattern is projected onto the scene. In theseembodiments, a first set of the three sets of images may correspond to a0° phase shift of the sinusoidal pattern, a second set of the three setsof images may correspond to 120° phase shift of the sinusoidal pattern,and a third set of the three sets of images may correspond to 240° phaseshift of the sinusoidal pattern. In some of these embodiments, each ofthe first, second, and third set of images may comprise a single image.Alternatively, each of the first, second and third set of images maycomprise three images—the first image in each of the three of sets ofimages may correspond to the red colour channel, the second image ineach of the three sets of images may correspond to the green colourchannel, and the third image in each of the three sets of images maycorrespond to the blue colour channel.

Returning to FIG. 3 , at block 306, the plurality of images captured atblock 304 are demodulated based on the illumination pattern and withrespect to a target section in the plurality of captured images. Thedemodulation at block 306 may be performed by the processing unit 230 ofthe system 200. The target section corresponds to one of: a portion ofthe scene on which the illumination pattern is selectively projectedwhile the plurality of images were captured, a portion of the scene atwhich the projected illumination pattern is resolvable, a portion of thescene with pixel depth values which satisfy, a predetermined range.

Returning to FIG. 3 , at block 308, an ambient light suppressed image ofthe scene is generated based on results of the demodulation. Thegeneration of the ambient light suppressed image may be performed by theprocessing unit 230 of the system 200.

In some embodiments, demodulating the plurality of images at block 306may produce a first image corresponding to the AC component and a secondimage correspond to the DC component. The AC component may correspond tothe alternating part of a demodulated signal associated with theplurality of images, and the DC component may correspond to the constantpart of the demodulated signal. In these embodiments, at block 308 thefirst image may be selected as the ambient light suppressed image of thescene. It will be appreciated that the demodulation may be performed,for example, using formulae (1) and (2) as presented above withreference to FIG. 1 . It will also be appreciated that other formulaenot explicitly discussed here may be used for obtaining the AC and DCcomponents of the signal, e.g. those associated with Discrete CosineTransform, Fourier transform, etc.

As mentioned above with reference to block 302, in some embodimentsprojecting the illumination pattern onto at least a portion of the sceneat block 302 may comprise only selectively projecting the illuminationpattern onto a selected portion of the field of view of the imagingunit. In these embodiment, the target section may correspond to aportion of the scene on which the illumination pattern is selectivelyprojected, and demodulating the plurality of images with respect to thetarget section at block 306 may be performed such that the ambient lightsuppressed image of the scene generated at block 308 only depicts one ormore elements included in the selected portion of the field of view ofthe imagine unit.

As mentioned above, in some embodiments the illumination pattern mayhave a predetermined spatial frequency. In these embodiments, capturingthe plurality of images of the scene at block 304 may be performed at apredetermined focal depth. The predetermined spatial frequency of theillumination pattern and the predetermined focal depth of the imagingunit in these embodiments may be selected such that the illuminationpattern is only resolvable within a certain distance from the focus ofthe imaging unit 220 of the system 200. In addition, the target sectionmay correspond to a portion of the scene at which the projectedillumination pattern is resolvable. Moreover, in these embodimentsdemodulating the plurality of images with respect to the target sectionat block 3061 may be performed such that the ambient light suppressedimage of the scene generated at block 308 only depicts one or moreelements included in field of view within the certain distance rangefrom the focus of the imaging unit 220 of the system 200.

Although not illustrated in FIG. 3 , in some embodiments the method mayfurther comprise analysing the plurality of images to determine 3D depthinformation of the scene. The 3D depth information may comprise depthvalues for each of the pixels of the plurality of images and in theseembodiments the target section may be based on the 3D depth informationof the scene. In this regard, the method may further comprisedetermining the target section by applying a phase mask to the pluralityof images captured at block 304.

Furthermore, in these embodiments generating the ambient lightsuppressed image of the scene at block 308 may be performed by onlyoutputting the demodulation results with respect to the target section.

FIG. 4 illustrates an ambient light suppression operation by way of anumber of images, according to an embodiment. The illustrated operationcan generally be performed by the system 200, and specifically in someembodiments by or under the control of processing unit 230 of the system200. For the purpose of illustration, at least parts of the operationillustrated in FIG. 4 will be described in the following with referenceto the various components of the system 200 of FIG. 2 .

As shown in FIG. 4 , there is provided a plurality of modulated images410A, 410B, and 410C, an AC component image 420, and a DC componentimage 430. The plurality of modulated images comprises a first modulatedimage 410A, a second modulated image 410B, and a third modulated image410C. The AC component image 420 may correspond to the alternating partof a demodulated signal, and the DC component 430 image may correspondto the constant part of the demodulated signal.

It can be seen for the present embodiment in each of the first modulatedimage 410A, the second modulated image 410B, and the third modulatedimage 410C, an illumination pattern is selectively projected by theimage projection unit 210 of the system 200 onto a selected(rectangular) portion. The illumination pattern is a time-varyingspatially modulated pattern. Specifically, in this embodiment, theillumination pattern consists of a plurality of alternate horizontaldark and bright bands.

In this embodiment, the selected portion onto which the illuminationpattern is projected corresponds to a portion of the field of view ofthe imaging unit 220 of the system 200, rather than all of the field ofview of the imaging unit 220. Moreover, each of the modulated images inthis embodiment have been captured at a different point in time thatcorresponds to a respectively different phase shift of the projectedillumination pattern. In the first modulated image 410A the illuminationpattern has a 0° phase shift, in the second modulated image 410A, theillumination pattern has a 120° phase shift, and in the third modulatedimage 410C, the illumination pattern has a 240° phase shift.

Once the modulated images 410A, 410B, and 410C have been captured, theprocessing unit 230 of the system 200 can demodulate the modulatedimages 410A, 410B, and 410C based on the illumination pattern depictedin these modulated images, as well as with respect to a target section,which in this embodiment corresponds to a portion of the scene on whichthe illumination pattern is selectively projected. Subsequently, theprocessing unit 230 can generate an ambient light suppressed image ofthe scene based on the results of the demodulation.

In more detail, the processing unit 230 can demodulate the modulatedimages 410A, 410B, and 410C with respect to the target section such thatthe generated ambient light suppressed image of the scene only depictsone or more elements included in the selected portion of the field ofview of the imaging unit 220. In other words, in this embodiment thegenerated ambient light suppressed image of the scene only depictselement(s) included in the rectangular portion onto which theillumination pattern is projected. The processing unit 230 candemodulate the modulated images 410A, 410B, and 410C to produce a firstimage corresponding to the AC component (i.e. AC component image 420)and a second image corresponding to the DC component (i.e. DC componentimage 430), where the AC component corresponds to the alternating partof a demodulated signal associated with the modulated images, and the DCcomponent corresponds to the constant part of the demodulated signal. Itwill be appreciated that the demodulation may be performed, for example,using formulae (1) and (2) as presented above with reference to FIG. 1 .It will also be appreciated that other formulae not explicitly discussedhere may be used for obtaining the AC and DC components of the signal,e.g. those associated with Discrete Cosine Transform, Fourier transform,etc.

In this case, the AC component image 420 is selected as the ambientlight suppressed image of the scene. Thus, elements that are in thescene of the modulated images but not in the selected portion can beexcluded in the ambient light suppressed image of the scene.

FIG. 5 illustrates an ambient light suppression operation by way of anumber of images, according to another embodiment. The illustratedoperation can generally be performed by the system 200, and specificallyin some embodiments by or under the control of processing unit 230 ofthe system 200. For the purpose of illustration, at least parts of theoperation illustrated in FIG. 5 will be described in the following withreference to the various components of the system 200 of FIG. 2 .

In the embodiment as illustrated in FIG. 5 , the image projection unit210 of the system 200 is configured to project an illumination patternhaving a predetermined spatial frequency. Furthermore, the imaging unit220 of the system 200 comprises a monochrome camera. The imaging unit220 is configured to capture the plurality of images of the scene at apredetermined focal depth, respectively for three different colourchannels (RGB). The predetermined spatial frequency of the illuminationpattern and the predetermined focal depth of the imaging unit areselected such that the illumination pattern is only resolvable within acertain distance from the focus of the imaging unit 220.

As shown in FIG. 5 , there is provided three sets of modulated imagesincluding a first set of modulated images 520-1, a second set ofmodulated images 520-2, and a third set of modulated images 520-3. Thefirst set of modulated images 520-1 corresponds to the blue colourchannel captured by the monochrome camera, the second set of modulatedimages 520-2 corresponds to the green colour channel captured by themonochrome camera, and the third set of modulated images 520-3corresponds to the red colour channel captured by the monochrome camera.Furthermore, in FIG. 5 there is also provided a normal image 510 whichrepresents an image of the scene depicted in the modulated images 520-1,520-2, and 520-3 captured in normal conditions with no illuminationpattern projected. In addition, a set of AC component images 530, a setof DC component images 540, and a resultant image 550 are provided inFIG. 5 .

As described with reference to FIG. 2 above, the illumination pattern isa time-varying spatially modulated pattern. Each of the three modulatedimages in each of the first, second, and third sets of modulated images520-1, 520-2, 520-3 in this embodiment have been captured at a differentpoint in time that corresponds to a respectively different phase shiftof the projected illumination pattern, for example each of these threeimages in a set may respectively corresponds to a point in time when theillumination pattern has a 0° phase shift, a point in time when theillumination pattern has a 120° phase shift, and a point in time whenthe illumination pattern has a 240° phase shift.

Furthermore, in this embodiment, the target section corresponds to aportion of the scene at which the projected illumination pattern isresolvable. As shown in FIG. 5 , by using the right combination of thepredetermined spatial frequency of the illumination pattern and thepredetermined focal depth of the imaging unit, there is a distance fromthe focused object in the scene for which the illumination patterncannot be resolved. In more detail, it can be seen for the presentembodiment in each image of each of the first set of modulated images520-1, the second set of modulated images 520-2, and the third set ofmodulated image 520-3, the projected illumination pattern (whichconsists of a plurality of alternate horizontal dark and bright bands)is only distinguishable on the round element and the pen, but not in thebackground (objects located more than 1 m from the focal depth) of thescene.

Once the three sets of modulated images 520-1, 520-2, 520-3 have beencaptured, the processing unit 230 of the system 200 can demodulate thethree sets of modulated images 520-1, 520-2, 520-3 based on theillumination pattern depicted in these modulated images, as well as withrespect to a target section, which in this embodiment corresponds to theportion of the scene at which the projected illumination pattern isresolvable. Subsequently, the processing unit 230 can generate anambient light suppressed image of the scene based on the results of thedemodulation.

In more detail, the processing unit 230 can demodulate each of the threesets of the modulated images 510-1, 520-2, 520-3 with respect to thetarget section to respectively generate three AC component images whichrespectively correspond to the blue colour channel, the green colourchannel, and the red colour channel. These three AC component imagesform the set of AC component images 530 as shown in FIG. 5 . Also, thedemodulation operation can also generate three DC component images whichrespectively correspond to the blue colour channel, the green colourchannel, and the red colour channel. These three DC component imagesform the set of DC components images 540 as shown in FIG. 5 . It will beappreciated that the demodulation may be performed, for example, usingformulae (1) and (2) as presented above with reference to FIG. 1 . Itwill also be appreciated that other formulae not explicitly discussedhere may be used for obtaining the AC and DC components of the signal,e.g. those associated with Discrete Cosine Transform, Fourier transform,etc.

In this case, the set AC component image 530 is selected andsubsequently processed (i.e. RGB reconstruction) to generate an ambientlight suppressed image 550 of the scene. Thus, elements that are in thebackground (with focal depth more than 1 m) of the scene of themodulated images can be excluded in the ambient light suppressed image550 of the scene. In other words, in this embodiment the generatedambient light suppressed image 550 of the scene only depicts element(s)included in the foreground at which the illumination pattern isresolvable.

FIG. 6 illustrate an ambient light suppression operation by way of anumber of images, according to another embodiment. The illustratedoperation can generally be performed by the system 200, and specificallyin some embodiments by or under the control of processing unit 230 ofthe system 200. For the purpose of illustration, at least parts of theoperation illustrated in FIG. 6 will be described in the following withreference to the various components of the system 200 of FIG. 2 .

Similar to the arrangement as illustrated in FIG. 5 , in the embodimentof FIG. 6 the image projection unit 210 of the system 200 is configuredto project an illumination pattern having a predetermined spatialfrequency. Furthermore, also similar to the arrangement as illustratedin FIG. 5 , in this embodiment the imaging unit 220 of the system 200comprises a monochrome camera. The imaging unit 220 is configured tocapture the plurality of images of the scene at a predetermined focaldepth, respectively for three different colour channels (RGB). Thepredetermined spatial frequency of the illumination pattern and thepredetermined focal depth of the imaging unit are selected such that theillumination pattern is only resolvable within a certain distance fromthe focus of the imaging unit 220.

As shown in FIG. 6 , there is provided three sets of modulated imagesincluding a first set of modulated images 610-1, a second set ofmodulated images 610-2, and a third set of modulated images 610-3. Thefirst set of modulated images 610-1 corresponds to the blue colourchannel captured by the monochrome camera, the second set of modulatedimages 610-2 corresponds to the green colour channel captured by themonochrome camera, and the third set of modulated images 610-3corresponds to the red colour channel captured by the monochrome camera.

As described with reference to FIG. 2 above, the illumination pattern isa time-varying spatially modulated pattern. Each of the three modulatedimages in each of the first, second, and third sets of modulated images610-1, 611-2, 610-3 in this embodiment have been captured at a differentpoint in time that corresponds to a respectively different phase shiftof the projected illumination pattern, for example each of these threeimages in a set may respectively corresponds to a point in time when theillumination pattern has a 0° phase shift, a point in time when theillumination pattern has a 120° phase shift, and a point in time whenthe illumination pattern has a 240° phase shift.

Furthermore, in this embodiment, the target section corresponds to aportion of the scene at which the projected illumination pattern isresolvable. As shown in FIG. 6 , by using the right combination of thepredetermined spatial frequency of the illumination pattern and thepredetermined focal depth of the imaging unit, there is a distance fromthe focused object in the scene for which the illumination patterncannot be resolved. In more detail, it can be seen for the presentembodiment in each image of each of the first set of modulated images610-1, the second set of modulated images 610-2, and the third set ofmodulated image 610-3, the projected illumination pattern (whichconsists of a plurality of alternate horizontal dark and bright bands)is only distinguishable on a rectangular object in the background of thescene.

Once the three sets of modulated images 610-1, 610-2, 610-3 have beencaptured, the processing unit 230 of the system 200 can demodulate thethree sets of modulated images 610-1, 610-2, 610-3 based on theillumination pattern depicted in these modulated images, as well as withrespect to a target section, which in this embodiment corresponds to theportion of the scene at which the projected illumination pattern isresolvable. Subsequently, the processing unit 230 can generate anambient light suppressed image of the scene based on the results of thedemodulation.

In more detail, the processing unit 230 can demodulate each of the threesets of the modulated images 610-1, 620-2, 620-3 with respect to thetarget section to respectively generate three AC component images whichrespectively correspond to the blue colour channel, the green colourchannel, and the red colour channel. Also, the demodulation operationcan also generate three DC component images which respectivelycorrespond to the blue colour channel, the green colour channel, and thered colour channel. In this case, the set AC component image can beselected and subsequently processed (i.e. RGB reconstruction) togenerate an ambient light suppressed image 620 of the scene. It will beappreciated that the demodulation may be performed, for example, usingformulae (1) and (2) as presented above with reference to FIG. 1 . Itwill also be appreciated that other formulae not explicitly discussedhere may be used for obtaining the AC and DC components of the signal,e.g. those associated with Discrete Cosine Transform, Fourier transform,etc.

Thus, elements that are in the foreground of the scene of the modulatedimages can be excluded in the ambient light suppressed image 620 of thescene. In other words, in this embodiment the generated ambient lightsuppressed image 620 of the scene only depicts certain element(s)included in the background at which the illumination pattern isresolvable.

Although it is described with reference to some embodiments above thateach set of modulated images corresponding to a colour channel comprisesthree images, it will be appreciated that in alternative embodimentseach set of modulated images may comprise fewer or more images,depending on for example the amount of time and resources available, themotion of the target or of the system itself, as well as a desired levelof ambient light suppression, etc.

FIG. 7 illustrates an ambient light suppression operation according toanother embodiment. The illustrated operation can generally be performedby the system 200, and specifically in some embodiments by or under thecontrol of processing unit 230 of the system 200. For the purpose ofillustration, at least parts of the operation illustrated in FIG. 7 willbe described in the following with reference to the various componentsof the system 200 of FIG. 2 .

As shown in FIG. 7 , there is provided a plurality of modulated images710. As described with reference to FIG. 2 above, the illuminationpattern is a time-varying spatially modulated pattern, thus each of theplurality of modulated images 710 in this embodiment may have beencaptured at a different point in time that corresponds to a respectivelydifferent phase shift of the projected illumination pattern.Furthermore, the illumination pattern in this embodiment furthercomprises at least one phase ramp of a predetermined step size.

Once the plurality of modulated images 7103 have been captured, theprocessing unit 230 of the system 200 can demodulate the modulatedimages based on the illumination pattern depicted in these modulatedimages, as well as with respect to a target section. As will beexplained in more detail in the paragraph below, the target section inthe present embodiment is based on 3D depth information of the scenedepicted in the plurality of modulated images 710.

In this embodiment, the processing unit 230 is configured to analyse theplurality of modulated images 710 to determine 3D depth information ofthe scene depicted. In more detail, a phase mask can applied to theplurality of modulated images 710—this operation is represented by thephase mask 720 in FIG. 7 , and is performed prior to the determinationof the 3D depth information of the scene. The 3D depth informationcomprises depth values for each of the pixels of the plurality ofmodulated images 710. Once the 3D depth information of the scene isdetermined, the processing unit 230 is configured to determine thetarget section based on the 3D depth information of the scene depicted.The 3D depth information of the scene is represented by the 3D depthmodel 730 as shown in FIG. 7 . As an example of the operation ofdetermining the target section in this embodiment, the processing unit230 may be configured to select one or more portions in the plurality ofmodulated images 710 that correspond to a predetermined range of 3Ddepth values, e.g. a portion corresponding to the face of a user.

Subsequently, the processing unit 230 can generate an ambient lightsuppressed image of the scene based on the results of the demodulation.Specifically, in this embodiment, the processing unit 230 is configuredto generate the ambient light suppressed image of the scene by onlyoutputting the demodulation results with respect to the target section.Thus, elements that are not depicted in the target section (e.g. if the3D depth values of the corresponding pixels do not fall within apredetermined range) can be excluded in the ambient light suppressedimage of the scene. In other words, in this embodiment the generatedambient light suppressed image of the scene only depicts certainelement(s) that fulfil certain criteria with respect to 3D depth values.

FIG. 8 illustrates a result of an ambient light suppression operationaccording to an embodiment compared with other imaging or processingtechniques.

For the purpose of reference, a normal image (without image processingor modulation) 810 is provided. As shown in the normal image 810, afirst element A, a second element B, and a third element C are depicted.The first to third elements A to C as depicted corresponds to a numberof different distances of the respective element to an imaging unit,with the first element A being closest to the imaging unit and the thirdelement C being furthest away from the imaging unit.

A blurred image 820 is provided next to the normal image 810. Theblurred image 820 represents a resultant image subsequent to performinga blurring processing on the normal image 810 as an attempt to removesome of the details depicted. In the example shown in the blurred image820, image processing is performed so as to remove details that are inthe background of the normal image 810, i.e. the third element C.

A first ambient light correction (ALC) image 830 is provided next to theblurred image 820. The first ALC image 830 represents a resultant imagesubsequent to performing a wide illumination ambient light correctionprocessing on the normal image 810 as an attempt to remove some of thedetails depicted. Similar to the blurred image 820 described above, inthe example shown in the first ALC image 830, image processing isperformed on modulated images so as to remove details that are in thebackground. Compared to simply performing blurring, it can be shown thatwide illumination ambient light correction is more effective in removingbackground details, e.g. the third element C.

Furthermore, a second ALC image 840 and a third ALC image 850 areprovided next, where the second ALC image 840 and the third ALC image850 represent resultant images subsequent to performing ambient lightsuppression operations as described in embodiments described herein.Specifically, in this embodiment illumination patterns are onlyselectively projected onto a selected portion of the field of view ofthe image unit while a plurality of modulated images are captured. Inthe example of the second ALC image 840, the selected portioncorresponds to a portion depicting the first element A, and in theexample of the third ALC image 850, the selected portion corresponds toa rectangular portion depicting a part of the first element A. Thus, thetarget section corresponds to a portion of the scene on which theillumination pattern is selectively projected.

In both of the examples presented by the second ALC image 840 and thethird ALC image 850, the modulated images are demodulated with respectto the respective target section, such that the respective generatedambient light suppressed image of the scene only depicts one or moreelements included in the selected portion of the field of view of theimaging unit. Accordingly, as shown in the second ALC image 840 and thethird ALC image 850, only element A is depicted and only a part ofelement A is depicted in the respective results.

There is thus provided an improved system for performing ambient lightsuppression and a method of controlling thereof. Embodiments describedherein allow improved suppression of background element(s) in images, ascompared to currently known techniques for shallow depth-of-fielddetection imaging (e.g. including blurring) or wide illumination ambientlight correction. This is because the techniques described herein offera better approach of removing out-of-focus portions from images as wellas an improved way to perform sub-selection of in-focus portions inimages.

There is also provided a computer program product comprising a computerreadable medium, the computer readable medium having computer readablecode embodied therein, the computer readable code being configured suchthat, on execution by a suitable computer or processor, the computer orprocessor is caused to perform the method or methods described herein.Thus, it will be appreciated that the disclosure also applies tocomputer programs, particularly computer programs on or in a carrier,adapted to put embodiments into practice. The program may be in the formof a source code, an object code, a code intermediate source and anobject code such as in a partially compiled form, or in any other formsuitable for use in the implementation of the method according to theembodiments described herein.

It will also be appreciated that such a program may have many differentarchitectural designs. For example, a program code implementing thefunctionality of the method or system may be sub-divided into one ormore sub-routines. Many different ways of distributing the functionalityamong these sub-routines will be apparent to the skilled person. Thesub-routines may be stored together in one executable file to form aself-contained program. Such an executable file may comprisecomputer-executable instructions, for example, processor instructionsand/or interpreter instructions (e g. Java interpreter instructions).Alternatively, one or more or all of the sub-routines may be stored inat least one external library file and linked with a main program eitherstatically or dynamically, e.g. at run-time. The main program containsat least one call to at least one of the sub-routines. The sub-routinesmay also comprise function calls to each other.

An embodiment relating to a computer program product comprisescomputer-executable instructions corresponding to each processing stageof at least one of the methods set forth herein. These instructions maybe sub-divided into sub-routines and/or stored in one or more files thatmay be linked statically or dynamically. Another embodiment relating toa computer program product comprises computer-executable instructionscorresponding to each means of at least one of the systems and/orproducts set forth herein. These instructions may be sub-divided intosub-routines and/or stored in one or more files that may be linkedstatically or dynamically.

The carrier of a computer program may be any entity or device capable ofcarrying the program. For example, the carrier may include a datastorage, such as a ROM, for example, a CD ROM or a semiconductor ROM, ora magnetic recording medium, for example, a hard disk. Furthermore, thecarrier may be a transmissible carrier such as an electric or opticalsignal, which may be conveyed via electric or optical cable or by radioor other means. When the program is embodied in such a signal, thecarrier may be constituted by such a cable or other device or means.Alternatively, the carrier may be an integrated circuit in which theprogram is embedded, the integrated circuit being adapted to perform, orused in the performance of, the relevant method.

Variations to the disclosed embodiments can be understood and effectedby those skilled in the art in practicing the principles and techniquesdescribed herein, from a study of the drawings, the disclosure and theappended claims. In the claims, the word “comprising” does not excludeother elements or steps, and the indefinite article “a” or “an” does notexclude a plurality. A single processor or other unit may fulfil thefunctions of several items recited in the claims. The mere fact thatcertain measures are recited in mutually different dependent claims doesnot indicate that a combination of these measures cannot be used toadvantage. A computer program may be stored or distributed on a suitablemedium, such as an optical storage medium or a solid-state mediumsupplied together with or as part of other hardware, but may also bedistributed in other forms, such as via the Internet or other wired orwireless telecommunication systems. Any reference signs in the claimsshould not be construed as limiting the scope.

The invention claimed is:
 1. A system for performing ambient lightsuppression, the system comprising: an image projection unit configuredto project an illumination pattern onto at least a portion of a scene,wherein the illumination pattern is a time-varying spatially modulatedpattern having a predetermined spatial frequency; an imaging unit havinga field of view, the imaging unit being configured to capture aplurality of images of the scene while the illumination pattern isprojected onto the scene; and a processing unit configured to:demodulate the plurality of images based on the illumination pattern andwith respect to a target section in the captured plurality of images,wherein the target section is a part of the field of view of the imagingunit and corresponds to one of: a portion of the scene on which theillumination pattern is selectively projected while the plurality ofimages were captured, a portion of the scene at which the projectedillumination pattern is resolvable, or a portion of the scene with pixeldepth values for pixels of the plurality of images which satisfy apredetermined range; and generate an ambient light suppressed image ofthe scene by suppressing ambient light based on results of thedemodulation.
 2. The system according to claim 1, wherein the imageprojection unit is configured to only selectively project theillumination pattern onto a selected portion of the field of view of theimaging unit, and the target section corresponds to a portion of thescene on which the illumination pattern is selectively projected, andwherein the processing unit is configured to demodulate the plurality ofimages with respect to the target section such that the generatedambient light suppressed image of the scene only depicts one or moreelements included in the selected portion of the field of view of theimaging unit.
 3. The system according to claim 1, wherein the processingunit is configured to analyse the plurality of images to determine 3Ddepth information of the scene, wherein the 3D depth informationcomprises the pixel depth value for each of the pixels of the pluralityof images and the target section is based on the 3D depth information ofthe scene, wherein the processing unit is configured to generate theambient light suppressed image of the scene by only outputting thedemodulation results with respect to the target section.
 4. The systemaccording to claim 3, wherein the processing unit is configured todetermine the target section by applying a phase mask to the pluralityof images.
 5. The system according to claim 1, wherein the time-varying,spatially modulated pattern comprises a phase-shifting sinusoidalpattern, and wherein the imaging unit is configured to capture theplurality of images at a predetermined phase difference with respect toa phase of the sinusoidal pattern.
 6. The system according to claim 1,wherein the illumination pattern further comprises at least one phaseramp of a predetermined step size.
 7. The system according to claim 1,wherein the time-varying spatially modulated pattern comprises aphase-shifting sinusoidal pattern, and wherein the imaging unit isconfigured to capture, while the illumination pattern is projected ontothe scene, three sets of images, wherein a first set of the three setsof images corresponds to a 0° phase shift of the sinusoidal pattern, asecond set of the three sets of images corresponds to 120° phase shiftof the sinusoidal pattern, and a third set of the three sets of imagescorresponds to 240° phase shift of the sinusoidal pattern.
 8. The systemaccording to claim 7, wherein the imaging unit comprises a colourcamera, and each of the first, second, and third set of images comprisesa single image.
 9. The system according to claim 7, wherein each of thefirst, second and third set of images comprises three images, wherein afirst image in each of the three of sets of images corresponds to a redcolour channel, a second image in each of the three sets of imagescorresponds to a green colour channel, and a third image in each of thethree sets of images corresponds to a blue colour channel.
 10. Thesystem according to claim 1, wherein the processing unit is configuredto demodulate the plurality of images to produce a first imagecorresponding to an AC component and a second image correspond to a DCcomponent, wherein the first image is selected as the ambient lightsuppressed image of the scene.
 11. A system for performing ambient lightsuppression, the system comprising: an image projection unit configuredto project an illumination pattern onto at least a portion of a scenewherein the illumination pattern is a time-varying spatially modulatedpattern having a predetermined spatial frequency; an imaging unit havinga field of view, the imaging unit being configured to capture aplurality of images of the scene while the illumination pattern isprojected onto the scene, wherein the imaging unit is configured tocapture the plurality of images of the scene at a predetermined focaldepth, the predetermined spatial frequency of the illumination patternand the predetermined focal depth of the imaging unit being selectedsuch that the illumination pattern is only resolvable within a certaindistance from a focus of the imaging unit; and a processing unitconfigured to: demodulate the plurality of images based on theillumination pattern and with respect to a target section in thecaptured plurality of images, wherein the target section is a part ofthe field of view of the imaging unit and corresponds to a portion ofthe scene at which the projected illumination pattern is resolvable; andgenerate an ambient light suppressed image of the scene based on resultsof the demodulation, wherein the processing unit is configured todemodulate the plurality of images with respect to the target sectionsuch that the generated ambient light suppressed image of the scene onlydepicts one or more elements included in the field of view within thecertain distance from the focus of the imaging unit.
 12. A method forcontrolling a system to perform ambient light suppression, wherein thesystem comprises an image projection unit, an imaging unit, and aprocessing unit, the method comprising: projecting, by the imageprojection unit, an illumination pattern onto at least a portion of ascene, wherein the illumination pattern is a time-varying spatiallymodulated pattern having a predetermined spatial frequency; capturing,by the imaging unit, a plurality of images of the scene while theillumination pattern is projected onto the scene; and demodulating, bythe processing unit, the plurality of images based on the illuminationpattern and with respect to a target section in the captured pluralityof images, wherein the target section is a part of a field of view ofthe imaging unit and corresponds to one of: a portion of the scene onwhich the illumination pattern is selectively projected while theplurality of images were captured, a portion of the scene at which theprojected illumination pattern is resolvable, a portion of the scenewith pixel depth values for pixels which satisfy a predetermined range;and generating, by the processing unit, an ambient light suppressedimage of the scene by suppressing ambient light based on results of thedemodulation.
 13. The method according to claim 12, wherein projectingthe illumination pattern onto at least a portion of the scene comprisesonly selectively projecting the illumination pattern onto a selectedportion of the field of view of the imaging unit, and wherein the targetsection corresponds to a portion of the scene on which the illuminationpattern is selectively projected, and wherein demodulating the pluralityof images with respect to the target section is performed such that thegenerated ambient light suppressed image of the scene only depicts oneor more elements included in the selected portion of the field of viewof the imaging unit.
 14. The method according to claim 12, whereincapturing the plurality of images of the scene is performed at apredetermined focal depth, wherein the predetermined spatial frequencyof the illumination pattern and the predetermined focal depth of theimaging unit are selected such that the illumination pattern is onlyresolvable within a certain distance from a focus of the imaging unit,and wherein the target section corresponds to a portion of the scene atwhich the projected illumination pattern is resolvable, and whereindemodulating the plurality of images with respect to the target sectionis performed such that the generated ambient light suppressed image ofthe scene only depicts one or more elements included in the field ofview within the certain distance from the focus of the imaging unit. 15.A non-transitory computer readable medium having computer readable codeembodied therein, the computer readable code being configured such that,on execution by a suitable computer or processor, the computer orprocessor is caused to perform the method according to claim
 12. 16. Themethod according to claim 12, further comprising: analyzing theplurality of images to determine 3D depth information of the scene,wherein the 3D depth information comprises the pixel depth values forthe pixels of the plurality of images and the target section is based onthe 3D depth information of the scene, wherein the ambient lightsuppressed image of the scene is generated by only outputting thedemodulation results with respect to the target section.
 17. The methodaccording to claim 16, further comprising: determining the targetsection by applying a phase mask to the plurality of images.
 18. Themethod according to claim 12, wherein the time-varying spatiallymodulated pattern comprises a phase-shifting sinusoidal pattern, andwherein the plurality of images are captured at a predetermined phasedifference with respect to a phase of the sinusoidal pattern.
 19. Themethod according to claim 12, wherein the time-varying spatiallymodulated pattern comprises a phase-shifting sinusoidal pattern, andwherein capturing the plurality of images of the scene while theillumination pattern is projected onto the scene comprises capturingthree sets of images, wherein a first set of the three sets of imagescorresponds to a 0° phase shift of the sinusoidal pattern, a second setof the three sets of images corresponds to 120° phase shift of thesinusoidal pattern, and a third set of the three sets of imagescorresponds to 240° phase shift of the sinusoidal pattern.
 20. Themethod according to claim 19, wherein each of the first, second andthird set of images comprises three images, wherein a first image ineach of the three of scats of images corresponds to a red colourchannel, a second image in each of the three sets of images correspondsto a green colour channel, and a third image in each of the three setsof images corresponds to a blue colour channel of the imaging unit.